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How Animals May Cause the Next Big One

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Jianan Yu/Reuters
A vendor sleeping at a poultry market in Hefei, Anhui province, March 2007, where a Chinese teenager died of bird flu the same month

In a revealing passage, Quammen roundly criticizes the science writer Richard Preston for narrative exaggeration. Preston’s The Hot Zone was a gripping account of an Ebola-like outbreak among lab monkeys in a corporate research facility in Reston, Virginia, in 1989. The book was a best seller and the basis for a movie starring Dustin Hoffman. “There’s no question that it did more than any journal article or newspaper story to make ebolaviruses infamous and terrifying to the general public,” Quammen says. The problem, he explains, is that the catalog of horrors described by Preston—liquefying organs, people dissolving in their beds—wasn’t quite accurate. But there’s important stuff Quammen himself leaves out. I would have appreciated a brief lesson in how anti-retroviral drugs work, as they have for many cases of HIV. If we continue to face threats from zoonoses, these treatments may be our best hope.

I also wish he’d spent more time talking about the coevolution of viruses and humans. Spillover leaves the impression that viruses are terribly scary. Quammen makes the qualifying point that sometimes they are neutral or even salubrious, but then he drops it. This doesn’t seem quite right. In fact, humans are part virus. Our genome carries about 100,000 fragments of retrovirus DNA, making up 8 percent of our total genetic material. As Carl Zimmer explains in A Planet of Viruses:

Many scientists now argue that viruses contain a genetic archive that’s been circulating the planet for billions of years. When they try to trace the common ancestry of virus genes, they often work their way back to a time before the common ancestor of all cell-based life.2

He notes that the French virologist Patrick Forterre has suggested that viruses may have “invented the double-stranded DNA molecule as a way to protect their genes from attack.” The mammalian placenta is made possible thanks to genes contributed by an ancient virus. Viral DNA is intertwined with ours and has been from our earliest beginnings. Viruses don’t just attack us; they are us.

If this is the case, and if, as we know, humans have been invading habitats since we left the cradle of Africa tens of thousands of years ago, how new a threat is zoonosis, really? After all, far fewer humans are dying of infectious disease than ever before. Quammen anticipates this criticism and has a convincing answer: HIV. That family of viruses has killed 30 million people worldwide and another 34 million are currently infected. Decades after its discovery, we still can’t effectively treat or contain it in many parts of the world. Uniquely modern factors, including changing sexual and social patterns, poor public health, and easy global transmission, amplified the pandemic. Aside from HIV, we penetrate more deeply and more destructively into remote ecosystems through large-scale mining operations, deforestation, oil and gas exploration, modern agriculture, and, of course, human-caused climate change.

World War I and globalization helped the Spanish flu become humankind’s worst viral outbreak. Despite its lethality rate of between one and two people per hundred infected, it ultimately killed around 50 million people. In the US, the virus was powerful enough to reduce the national average lifespan by ten years. More recently at home, West Nile virus infections were up 19 percent last summer. The Washington Post reported that the virus appears to be mutating to stronger strains capable of damaging the central nervous system. Mosquitoes, bearers of so many bad tidings for the human immune system, thrive in hotter, wetter places and longer warm seasons.

In an interview Charlie Calisher, a retired professor of microbiology at Colorado State University, tells Quammen that he found himself interested in bats after SARS, but he didn’t “know shit about immunology.” So he recruited some colleagues and together they wrote an important paper on why bats have turned out to be a vast reservoir for so many of the viruses that do us harm. Bats, Calisher explains, are abundant (one in four mammals is a bat) and very social. “Many kinds roost in huge aggregations that can include millions of individuals at close quarters,” Quammen writes. Furthermore, “it’s not insignificant that bats fly,” spreading their infections around to new populations. Does this sound familiar? It should, because it sounds a lot like us.

  1. 2

    University of Chicago Press, 2011, p. 93. 

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